The present invention generally relates to a wafer cassette for storing wafers and more particularly, relates to a wafer cassette pod for storing wafers that is equipped with a position sensing device for ensuring proper positioning on a loadport.
In the manufacturing of a semiconductor device, the device is usually processed at many work stations or processing machines. The transporting or conveying of a partially finished device, or a work-in-process (WIP) part, is an important aspect in the total manufacturing process. The conveying of semiconductor wafers is especially important in the manufacturing of integrated circuit chips due to the delicate nature of the chips. Furthermore, in fabricating an IC product, a multiplicity of fabrication steps, i.e. as many as several hundred, is usually required to complete the fabrication process. A semiconductor wafer or IC chips must be stored or transported between various process stations in order to perform various fabrication processes.
For instance, to complete the fabrication of an IC chip, various steps of deposition, cleaning, ion implantation, etching and passivation steps must be carried out before an IC chip is packaged for shipment. Each of these fabrication steps must be performed in a different process machine, i.e. a chemical vapor deposition chamber, an ion implantation chamber, an etcher, etc. A partially processed semiconductor wafer must be conveyed between various work stations many times before the fabrication process is completed. The safe conveying and accurate tracking of such semiconductor wafers or work-in-process parts in a semiconductor fabrication facility is therefore an important aspect of the total fabrication process.
Conventionally, partially finished semiconductor wafers or WIP parts are conveyed in a fabrication plant by automatically guided vehicles or overhead transport vehicles that travel on predetermined routes or tracks. For the conveying of semiconductor wafers, the wafers are normally loaded into cassettes pods, such as SMIF (standard machine interface) or FOUP (front opening unified pod), and then picked up and placed in the automatic conveying vehicles. For identifying and locating the various semiconductor wafers or WIP parts being transported, the cassettes or pods are normally labeled with a tag positioned on the side of the cassette or pod. The tags can be read automatically by a tag reader that is mounted on the guard rails of the conveying vehicle.
An OHT system is frequently used to deliver a cassette pod such as a FOUP to a process machine. This is shown in FIG. 1. A cassette pod 10 of the FOUP type is positioned on a loadport 12 of a process machine 14. The loadport 12 is equipped with a plurality of locating pins 16 for the proper positioning of the cassette pod 10. A detailed perspective view of the FOUP 10 is shown in FIG. 2. The FOUP 10 is constructed by a body portion 18 and a cover portion 28. The body portion 18 is provided with a cavity 46 equipped with a multiplicity of partitions 48 for the positioning of 25 wafers of the 300 mm size. The body portion 18 is further provided with sloped handles 50 on both sides of the body for ease of transporting. On top of the body portion 18, is provided with a plate member 52 for gripping by a transport arm (not shown) of the OHT system (not shown).
FIG. 3 is a side view of a conventional loadport with a FOUP positioned on top for loading wafer into a process machine.
The loadport 30 is part of a semiconductor process equipment 32 which includes a cassette door opener 54 for opening cassette door 34 and for accessing a wafer cassette pod, i.e. a FOUP 60. Problems in operating the FOUP cassette door frequently occurs when the door is not latched in an open position and thus, may accidentally drop onto the wafers which are not properly positioned. The falling cassette door can easily break the wafers when contacted with an impact force. This occurs when the FOUP is not properly docked on the loadport, or when the cassette door is not properly attached to the FOUP.
It is therefore an object of the present invention to provide a wafer cassette pod for docking onto a loadport that does not have the drawbacks or shortcoming of the conventional cassettes.
It is another object of the present invention to provide a wafer cassette pod for docking onto a loadport wherein the accidental falling of a cassette door on the wafers can be avoided.
It is a further object of the present invention to provide a wafer cassette pod that is equipped with at least one position sensing device for preventing breakage of wafers by the cassette door.
It is another further object of the present invention to provide a wafer cassette pod that is equipped with at least one position sensing device capable of separating the cassette from the docking door when the cassette is not properly positioned.
It is still another object of the present invention to provide a wafer cassette pod that is equipped with at least one spring-loaded position sensing device mounted in the sidewall of the cassette with fingers exposed.
In accordance with the present invention, a wafer cassette pod that is equipped with a position sensing device for preventing wafer breakage by a falling cassette door is provided.
In a preferred embodiment, a wafer cassette pod that is equipped with a position sensing device is provided which includes a cassette pod body formed of a top panel, a bottom panel, a front panel and two side panels; a rear opening in the cassette pod body formed by the top panel, the bottom panel and the two side panels for receiving wafers therethrough, the two side panels further include recessed slots on inside surfaces for positioning the wafers; and at least two spring-loaded position sensing devices each mounted in one of the two side panels with a finger protruding beyond an end surface of the side panel to push the cassette pod body away from a loadport of a process machine when the cassette pod body is not properly positioned on the loadport.
In the wafer cassette pod that is equipped with a position sensing device, the at least two spring-loaded position sensing devices are four position sensing devices with two mounted in each side panel. The at least two spring-loaded position sensing devices may each include a case that has an opening on a front side; a finger protruding through the opening of the case; and at least one spring pushing the finger outwardly away from the case. The two spring-loaded position sensing devices are mounted in a side panel with one near the top and the other near the bottom. Each of the at least two spring-loaded position sensing devices is further equipped with a connecting node mounted on the finger for making electrical connection with a sensor and for sending out a signal to a process controller when the connection is not made.
In the wafer cassette pod equipped with a position sensing device, the two side panels may further include slot openings in the end surface for mounting the at least two spring-loaded position sensing devices. The two side panels may further include slot openings in the end surface for frictionally engaging the at least two spring-loaded position sensing devices. The at least two spring-loaded position sensing devices each equipped with a spring that has a spring constant sufficiently large to push a fully loaded wafer cassette pod away from an opening of the loadport. The finger on the position sensing device may be loaded by two springs, or may be loaded by three springs.